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IC 8916 



Bureau of Mines Information Circular/1983 




Podiform Chromite Occurrences 
in the Caribou Mountain and Lower 
Kanuti River Areas, Central Alaska 



Part II: Beneficiation 



By D. C. Dahlin, L. L. Brown, and J. J. Kinney 




UNITED STATES DEPARTMENT OF THE INTERIOR 



Information Circular 8916 



Podiform Chromite Occurrences 
in the Caribou Mountain and Lower 
Kanuti River Areas, Central Alaska 



Part II: Beneficiation 



By D. C. Dahlin, L. L. Brown, and J. J. Kinney 





UNITED STATES DEPARTMENT OF THE INTERIOR 
James G. Watt, Secretary 

BUREAU OF MINES 
Robert C. Horton, Director 



\8?. 



tf* 



<V&«^ 



This publication has been cataloged as follows: 




Podiform chromite occurrences in the Caribou Mountain and Lower Ka- 
nuti River areas, centra) Alaska. 

(Information circular ; 8916) 

Includes bibliographies. k 

Supt. of Docs, no.: I 28.27:8916. 

Contents: pt. 1. Reconnaissance investigations / by Jeffrey Y. 
Foley and Mark M. McDermott— pt. 2. Beneficiation / by D. C. Dah- 
lin, 1-. I-. Brown, and J. J. Kinney. 

1. Chromite— Alaska. 2. Prospecting— Alaska. I. Foley, Jeffrey 
Y. II. Series: Information circular (United States. Bureau of Mines) ; 
8916. 

Tfm5rW4-fW4#0rG4} 622s [553.4'643'097986] 82-600286 



CONTENTS 

Page 

Abstract 1 

Introduction 2 

Acknowledgments 2 

Mineralogy 3 

Benef iciation procedure 5 

Results and discussion 7 

Summary and conclusions 9 

Appendix. — Metallurgical balances 10 

ILLUSTRATIONS 

1. General benef iciation procedure used to concentrate 11 lower Kanuti 

River and Caribou Mountain samples 5 

2. General procedure for the electrodynamic separation step of the benef i- 

ciat ion procedure 6 



TABLES 

1. Head analyses of 11 chromite-bearing samples from the lower Kanuti River 

and Caribou Mountain areas of central Alaska 3 

2. Estimated mineral composition of 11 lower Kanuti River and Caribou Moun- 

tain samples 4 

3. Analyses of high-purity concentrates prepared from 100- by 200-mesh size 

fractions 4 

4. Summary of the calculated composite concentrates from benef iciation of 

11 chromite-bearing samples from the lower Kanuti River and Caribou 

Mountain areas 8 

A-l. Gravity concentration and electrodynamic separation of sample A 10 

A-2. Gravity concentration and electrodynamic separation of sample B 10 

A-3. Gravity concentration and electrodynamic separation of sample C 11 

A-4. Gravity concentration and electrodynamic separation of sample D 11 

A-5. Gravity concentration and electrodynamic separation of sample E 12 

A-6. Gravity concentration and electrodynamic separation of sample F 12 

A-7. Gravity concentration and electrodynamic separation of sample G 13 

A-8. Gravity concentration and electrodynamic separation of sample H 13 

A-9. Gravity concentration and electrodynamic separation of sample I 14 

A-10. Gravity concentration and electrodynamic separation of sample J 14 

A-ll. Gravity concentration and electrodynamic separation of sample K. 15 



PODIFORM CHROMITE OCCURRENCES IN THE CARIBOU MOUNTAIN 
AND LOWER KANUTI RIVER AREAS, CENTRAL ALASKA 

Part II: Beneficiation 

By D. C. Dahlin, 1 L. L. Brown, 2 and J. J. Kinney 3 



ABSTRACT 

The Bureau of Mines has investigated podiform chromite deposits in 
three ultramafic bodies in the Caribou Mountain and lower Kanuti River 
areas of central Alaska. The investigation, reported in two parts, was 
done as part of the Bureau's mission to help insure an adequate supply 
of minerals to meet the Nation's needs. Part I describes an extensive 
field investigation and mineralogical studies by personnel from the Bu- 
reau's Alaska Field Operations Center. This report, part II, describes 
the mineralogy of 11 samples that were high-graded from surface expo- 
sures at 10 sites and presents the results of laboratory batch benefi- 
ciation tests designed to concentrate the chromite. 

The 11 samples, peridotites and chromitites that consisted of vari- 
able amounts of chromite or chromium-bearing spinels, olivine, and ser- 
pentine, were beneficiated by grinding and sizing, gravity concentra- 
tion, and electrodynamic separation. Three high-chromium chromite con- 
centrates , two high-iron chromite concentrates , and one high-aluminum 
chromite concentrate were produced. Three other concentrates were mar- 
ginal, and two were submarginal. Chromium recoveries ranged from 
54 to 92 pet. These results indicate that the areas may be significant 
chromium resources . 

Potential platinum association with the chromite was also investi- 
gated. Analysis of these 11 samples indicates that the areas are not 
good platinum resources. 

^Metallurgist. 

■'Group supervisor and geologist. 

•^Geologist. 

All authors are with the Albany Research Center, Bureau of Mines, Albany, Oreg, 



INTRODUCTION 



The United States has no domestic pro- 
duction or economic reserves of chromite, 
the only commercial ore of chromium, and 
must rely on imports and on stockpiles to 
meet national needs. Although world re- 
serves of chromite are adequate to meet 
forecast world demand, sensitive politi- 
cal and economic considerations, as well 
as geographical location, could conceiv- 
ably make the United States vulnerable in 
an emergency. ^ The known large, high- 
grade chromite deposits are in the East- 
ern Hemisphere, and chromite imports have 
been primarily from the Republic of South 
Africa, the Soviet Union, the Philip- 
pines, Finland, and Turkey. As a means 
of meeting a potential emergency, the Bu- 
reau of Mines is characterizing potential 
domestic sources and developing process- 
ing technology. 

Chromium is used primarily in the met- 
allurgical industry, but also in the 
chemical and refractory industries. 
There are no economical substitutes for 
it in stainless steels and many other 
ferrous and nonferrous alloys. Chemical 
applications include plating, pigment 
production, and leather tanning. Chro- 
mite refractories are used in high- 
temperature applications such as furnace 
and kiln linings and as molding material 
in foundaries. 



Identified U.S. chromite resources in 
Montana and the Pacific Coast States are 
small, low-grade, or both. The largest 
deposit is in the Stillwater Complex, 
Mont., and contains a high-iron variety 
of chromite. Laterites from northern 
California and southwestern Oregon are a 
large, low-grade resource that the Bureau 
is currently investigating for chromite 
recovery. 5 

Geologists at the Bureau's Alaska Field 
Operations Center have done reconnais- 
sance investigations of three ultramafic 
complexes in the Caribou Mountain- 
Melozitna ultramafic belt in central 
Alaska. Their study is part I of this 
two-part investigation. 6 Geochemical 
sampling of the three complexes , iden- 
tified as the Caribou Mountain, upper 
Kanuti River, and lower Kanuti River ul- 
tramafic bodies, was used to describe the 
occurrences of chromite and examine the 
significance of Cr, Ni, and Co anomalies 
reported by earlier workers. This re- 
port, part II of the investigation, de- 
scribes the mineralogy and benef iciation 
of 11 chromite-bearing samples taken from 
10 sites within the three ultramafic 
bodies. 



ACKNOWLEDGMENTS 



The authors gratefully acknowledge the 
assistance of Jeff Foley, Mark McDermott, 

horning, J. L. , N. A. Matthews, and 
E. C. Peterson. Chromium. Ch. in Min- 
eral Facts and Problems, 1980 Edition. 
BuMines Bull. 671, 1981, pp. 167-182. 

5 Kirby, D. E., D. R. George, and C. B. 
Daellenbach. Chromium Recovery From 
Nickel-Cobalt Later ite and Later ite Leach 
Residue. BuMines RI 8676, 1982, 22 pp. 



and Karen Clautice, geologists, Alaska 
Field Operations Center, Bureau of 
Mines , in obtaining samples for this 
investigation. 

6 Foley, J. Y., and M. M. McDermott. 
Podiform Chromite Occurrences in the 
Caribou Mountain and Lower Kanuti River 
Areas, Central Alaska. Part I: Recon- 
naissance Investigations. BuMines 
IC 8915, 1983. 



MINERALOGY 



Each sample of chromite-bearing mate- 
rial that was studied was high-graded 
from surface exposures at the field site. 
The samples were high-graded to determine 
whether precious metals were associated 
with the chromite. The bulk samples of 
hard rock were collected from frost-riven 
rubble or from discontinuous pods and 
stringers in small outcrops and in shal- 
low subcrops, usually along ridge crests. 
Sample weight ranged from 10 to 350 lb, 
and maximum rock size in each sample 
ranged from 1 to 15 in. in the largest 
dimension. 

Representative specimens were selected 
from each sample for petrographic exami- 
nation. The samples ranged from hard, 
unweathered, massive chromite to chro- 
mite that was disseminated sparsely to 
densely in lenses and stringers less than 
an inch to several inches thick. Most 
of the samples had surface alteration 
from weathering, and most were highly 
fractured. 

All of the samples were mineralogically 
similar. They were peridotites and chro- 
mitites that consisted essentially of 
variable amounts of chromite or chromium- 
bearing spinels, olivine, and serpentine. 
Minor constituents included magnetite, 
chlorite, and f erromagnesian silicate 
minerals (pyroxenes and amphiboles) . Six 
samples contained traces of pyrite, 
and a trace of maucherite (Ni 3 As 2 ) was 



identified in sample E. Some of the oli- 
vine was altered to serpentine, and some 
of the serpentine and ferromagnesian sil- 
icates were altered to chlorite. 

Head analyses of the samples are shown 
in table 1. The samples are identified 
by the letters A through K, as they are 
in part I. The Cr 2 03 content of the sam- 
ples ranged from 13.2 to 47.2 pet. Plat- 
inum was reported in the head analysis of 
sample B at a grade of 0.039 oz/ton, but 
the platinum analysis of the other head 
samples was less than the minimum de- 
tection level. The sensitivity of the 
precious-metals analyses depends on the 
chromium content of the sample being ana- 
lyzed. The levels of detection are 0.01 
oz/ton for Pt , Pd, and Ag, and 0.002 
oz/ton for Au for a sample that contains 
more than about 20 pet Cr 2 03. For a sam- 
ple with less than about 20 pet Cr 2 3 , 
the levels of detection are improved to 
0.004 oz/ton for Pt and Pd and 0.0008 
oz/ton for Au, and remain at 0.01 oz/ton 
for Ag. All of the precious-metals anal- 
yses were done by a fire assay-atomic ab- 
sorption technique. 

In one case, samples taken from the 
same site were significantly different, 
as can be seen by comparing the analysis 
of sample I with that of sample J. Dif- 
ferences could also be seen in the hand 
specimens. The chromite in sample I was 



TABLE 1. - Head analyses of 11 chromite-bearing samples from the lower 
Kanuti River and Caribou Mountain areas of central Alaska 



Sample 


Chromite 
occurrence 1 




Analysis, 


pet 




Analysis , 


oz/ton 






Cr 2 3 


Fe 


MgO 


A1 2 3 


Si0 2 


Pt 


Pd 


Au 


Ag 


A 


3 


17.0 


8.5 


34.5 


4.1 


26.8 


<0.004 


<0.004 


<0.001 


0.04 


B 


6 


22.7 


20.7 


13.9 


22.6 


4.7 


.039 


.011 


<.001 


.10 


C 


7 


14.8 


9.3 


28.1 


8.4 


26.0 


<.004 


<.004 


.001 


.05 


D 


12 


31.1 


12.5 


22.1 


7.5 


14.9 


<.01 


<.01 


<.002 


.13 


E 


17 


47.2 


14.4 


13.7 


7.8 


7.0 


<.01 


<.01 


.003 


.45 


F 


18 


13.2 


10.8 


27.9 


16.2 


20.2 


<.01 


<.01 


<.002 


.03 


G 


19 


44.4 


18.6 


12.8 


7.6 


7.3 


<.01 


<.01 


<.002 


.05 


H 


20 


38.6 


18.7 


13.4 


10.7 


5.7 


<.01 


<.01 


<.002 


.05 


I 


21 


24.8 


15.8 


15.6 


30.5 


2.8 


<.01 


<.01 


.002 


.04 


J 


21 


15.6 


9.4 


27.2 


8.9 


25.8 


<.004 


<.004 


<.001 


.05 


K 


22 


20.3 


18.1 


17.0 


24.3 


6.6 


<.004 


<.004 


<.001 


.05 



Chromite occurrence locations are shown in part I. 



massive chromite, while in sample J, the 
chromite was disseminated in thin bands. 

Detailed mineralogical examinations 
were done on table concentrates and tail- 
ings from sized fractions. Binocular and 
petrographic microscopy and magnetic sep- 
aration techniques were used to determine 
the mineral composition of the samples. 
The composition of each sample appeared 
to be nearly uniform from one size frac- 
tion to the next. The 100- by 200-mesh 
fraction was studied because it was rep- 
resentative of the whole sample, and most 
of the mineral components were liberated 
in that size range. Table 2 shows the 
mineral composition, based on weight, of 
the samples, as calculated from the esti- 
mated compositions of the concentrates 
and tailings from the 100- by 200-mesh 
fraction. 



High-purity chromite concentrates were 
prepared by carefully controlled magnetic 
separation of table concentrates that had 
been submitted for detailed mineralogical 
examination. Each sample was fraction- 
ated at several electromagnetic field 
settings on a laboratory-model isodynamic 
separator. The best concentrate, as de- 
termined with a binocular microscope, was 
submitted for chemical analysis. Table 3 
shows the analyses of these high-purity 
concentrates from the samples. All were 
classified as magnesian aluminian chro- 
mites except samples B, F, I, and K. 
Those were identified as magnesian chro- 
mohercynites, iron-aluminum spinels 
(FeAl 2 4 ) that contain significant 
amounts of chromium and magnesium substi- 
tuted for aluminum and iron. 



TABLE 2. - Estimated mineral composition of 11 lower Kanuti River 
and Caribou Mountain samples , weight-percent 



Sample 


Chromite 


Olivine 


Serpentine 


Magnetics 1 


Chlorite 


Fer romagnes ian 
silicates 


Sulfides 


A 


26 


58 


14 


2 


Trace 


Trace 


Trace 


B 


81 


14 


Trace 


5 


Trace 


ND 


ND 


C 


27 


30 


25 


11 


3 


7 


ND 


D 


60 


20 


16 


3 


Trace 


Trace 


ND 


E 


79 


2 


12 


7 


Trace 


Trace 


Trace 


F 


31 


11 


46 


11 


2 


ND 


Trace 


G 


74 


Trace 


19 


6 


Trace 


ND 


ND 


H 


74 


ND 


16 


11 


Trace 


ND 


Trace 


I 


82 


Trace 


5 


10 


3 


ND 


ND 


J 


31 


23 


34 


s 10 


Trace 


2 


Trace 


K 


62 


13 


15 


10 


Trace 


ND 


ND 



ND Not detected. 'Minerals removable with a hand magnet. 

TABLE 3. - Analyses of high-purity concentrates prepared 
from 100- by 200-mesh size fractions 



Sample 






Analysis, 


pet 






Cr:Fe 




Cr 2 3 


Fe 


MgO 


A1 2 3 


Si0 2 


S 


P 


ratio 


A 


51.6 


15.6 


12.4 


12.0 


2.58 


0.009 


0.06 


2.3 


B 


24.8 


22.4 


12.0 


24.9 


1.79 


.011 


.05 


.8 


C 


38.9 


15.3 


14.3 


20.2 


3.92 


.011 


.17 


1.7 


D 


49.3 


15.9 


13.4 


12.3 


2.63 


.006 


.14 


2.1 


E 


53.8 


15.1 


11.4 


9.3 


3.61 


.009 


.05 


2.4 


F 


31.0 


16.1 


17.1 


27.1 


2.82 


.012 


.05 


1.3 


G 


52.9 


20.5 


10.3 


8.5 


1.58 


.009 


.12 


1.8 


H 


45.7 


20.5 


10.5 


13.8 


1.11 


.006 


.06 


1.5 


I 


27.5 


16.0 


14.8 


33.8 


.18 


.004 


.07 


1.2 


J 


39.8 


15.8 


13.9 


20.2 


3.62 


.009 


.09 


1.7 


K 


24.7 


20.0 


11.4 


31.6 


1.57 


.006 


.07 


.8 



BENEFICIATION PROCEDURE 



The benef iciation procedure that was 
used to produce a composite chromite con- 
centrate was essentially the same for 
each of the 11 samples and is shown in 
figure 1. Minor variations were adopted 
to the procedure to suit each individual 
sample. 

The samples, as received, consisted of 
hard, angular rock fragments from 1 to 
15 in. in the largest dimension. Each 
sample was crushed in a jaw crusher and 
screened to minus 1/4 in. A head sample 



and several 20-lb splits for beneficia- 
tion tests were prepared from the minus 
1/4-in material. 

For each sample, a split was screened 
on 48, 100, and 200 mesh. The plus 
48-mesh fraction was ground dry in a 
13- by 25-in rodmill and a 7- by 9-in 
rodmill to pass 48 mesh and was sized at 
100 and 200 mesh. Grinding was done in 
stages to minimize production of fines. 
Generally, the plus 48-mesh fraction from 
a 20-lb split was first ground in the 



Bulk sample 



Jaw crusher 



Plus 48 mesh 

1 

Rodmill 



48 by 100 mesh 

I 

Sand table 



Concentrate 



Tai 



Minus 1/4 in 

1 

-♦Screen 



Minus 48 mesh 



Screens 



100 by 200 mesh 

I 

Slime table 



ings Concentrate 



Middlings 
Dryer 



Midd 



Tai 



Minus 200 mesh 

1 

Slime table 



ings 



Concentrate Tai 



ings 



ings 



T 

Electrodynamic separator 

i r 



T 



Concentrate Middlings Tailings 



*-Dryer 

Electrodynamic separator 

i i r 

Concentrate Middlings Tailings 



FIGURE 1. - General beneficiation procedure used to concentrate 11 lower Kanuti River and 
Caribou Mountain samples. 



large mill in two stages of 5 and 3 min, 
and then, if needed, the remaining sample 
was ground in one to four stages of 3 min 
each in the small mill to reduce it to 
essentially 100 pet minus 48 mesh. The 
size splits were chosen because mineral 
liberation was good at 48 mesh and 
because 200 mesh approaches the lower 
practical limit of efficient separation 
by gravity and electrodynamic process- 
ing. The additional split at 100 mesh 
gave closely sized feed for gravity 
concentration. 

The three products were passed sepa- 
rately over a 2- by 4-ft laboratory shak- 
ing table. The 48- by 100-mesh fraction 
was fed to a sand deck, and the 100- by 
200-mesh fraction and the minus 200-mesh 
fraction were fed to a slime deck. A 
finished high-grade table concentrate was 
produced from each size fraction. De- 
pending on the grade and separation char- 
acteristics of the sample, a middlings 
product, a tailings product, or both were 
collected for further processing to im- 
prove recovery. In the cases where a 
middlings product was separated, barren 
tailings were discarded. Only a high- 
grade concentrate and tailings were pro- 
duced from the minus 200-mesh fraction. 
The minus 200-mesh concentrate contained 
only the coarser, high-specific-gravity 
particles of the size fraction. Several 
of the samples had relatively high chro- 
mite losses in the minus 200-mesh tail- 
ings because tabling becomes less effec- 
tive in separating very fine-sized parti- 
cles. The water that discharged off the 
tailings end of the table was dark brown, 
an indication that it contained very fine 
suspended chromite. Very fine chromite 
settled out in the tailings discharge 
tray. 

Middlings products, and those tail- 
ings products from tests where no mid- 
dlings products were taken, were dried 
and treated electrodynamically on a 
laboratory-model high-tension separator. 
A single layer of particles was fed onto 
a 14-in rotor by a vibratory feeder. The 
positions of the two electrodes were the 
same for all of the tests. The first 



electrode was oriented to give a combina- 
tion pinning and lifting effect, and the 
second electrode was oriented to give a 
lifting effect. Chromite and other con- 
ductors present were thrown from the ro- 
tor, while the olivine, serpentine, and 
other nonconductor gangue minerals were 
pinned to the rotor. Rotor speed was 
varied, and the splitters were adjusted 
to produce good concentrate, middlings, 
and tailings products. 

The general procedure for the electro- 
dynamic separation is shown in figure 2. 
The dry feed was separated into a con- 
centrate, middlings, and tailings. The 
middlings were retreated in two or more 
rougher steps. The concentrates from the 
three rougher passes were combined, and a 
cleaner step was done in which a cleaner 
concentrate and cleaner tailings were 
produced. The cleaner middlings were 
combined with the cleaner concentrate. 
The tailings from the three rougher 
passes were combined, and a scavenger 
step was done in which a scavenger con- 
centrate and scavenger tailings were pro- 
duced. The scavenger middlings were com- 
bined with the scavenger tailings. In 
industrial practice the scavenger concen- 
trate, third rougher middlings, and 
cleaner tailings would probably be com- 
bined and recirculated to the head of the 
electrodynamic separation circuit. 

The procedure for electrodynamic sepa- 
ration was modified to suit the samples. 



Dry table middlings 

I 
First rougher electrodynamic separation 

•Concentrate Middlings Tailings- 



T 

Second rougher electrodynamic separation 

J I I 
-Concentrate Middlings Tailings 

— r~ 

Thi-d rougher electrodynamic separation 
J J —J— 

-Concentrate Middlings Tailings 



Cleaner electrodynamic separation Scavenger electrodynamic separation 
I J J f— 

Cleaner Cleaner Scavenger Scavenger 

concentrate tailings concentrate tailings 

FIGURE 2. - General procedure for the electrody- 
namic separation step of the beneficiation procedure. 



Three rougher steps were impractical on 
several middlings and tailings samples 
that were relatively small; one or two 
steps were sufficient. The cleaner and 
scavenger steps were omitted on sev- 
eral of the smaller samples. The minus 
200-mesh table tailings were not treated 
electrodynamically because the process is 
not effective in that size range. 

Electrodynamic separation was done pri- 
marily to give an indication of the 
increased recovery of chromite attain- 
able from table middlings or tailings. 
Optimum separation parameters were not 
investigated. A limited number of vari- 
ations in conditions were investigated 
for each sample, and those that gave 
good products, as determined visually, 
were used. 



A magnetic separation step was not in- 
cluded in this process flowsheet , al- 
though low-intensity wet magnetic separa- 
tion was considered as a means to improve 
the Cr:Fe ratio by removing magnetite. 
The mineralogy of the samples indicated 
that the table concentrates contained 
2 to 15 pet magnetics as particles remov- 
able with a hand magnet. Attempts to re- 
move a magnetic fraction from several ta- 
ble concentrates were ineffective with a 
laboratory-model concurrent wet drum mag- 
netic separator with a permanent magnet. 
A very small percentage of the expected 
weight of magnetics was removed. A 
larger magnetic fraction could be removed 
with a higher intensity magnetic field at 
the expense of chromite recovery. 



RESULTS AND DISCUSSION 



The calculated composite chromite con- 
centrates that were produced from the 
lower Kanuti River and Caribou Mountain 
ultramafics may be categorized in one of 
the following groups :^ 

1. High-chromium (metallurgical-grade) 
chromite that contains a minimum of 
46 pet Cr203 with a Cr:Fe ratio greater 
than 2.0:1. 

2. High-iron (chemical-grade) chromite 
that contains 40 to 46 pet Cr20 3 with a 
Cr:Fe ratio of 1.5:1 to 2.0:1. 

3. High-aluminum (refractory-grade) 
chromite that contains more than 20 pet 
AI2O3 and more than 60 pet AI2O3 plus 
Cr 2 3 . 

4. Marginal chromite that meets either 
the grade or Cr:Fe-ratio requirement for 
one of the classifications above and very 
nearly meets the other. 

5. Submarginal chromite that fails to 
meet the above classifications. 



'Categories 1, 2, and 3 are from work 
cited in footnote 4. 



Table 4 summarizes the results of bene- 
ficiation of the 11 samples using the 
procedure in figure 1. Complete metal- 
lurgical balances may be found in 
tables A-l through A-ll in the appendix. 

Samples A, D, and E were beneficiated 
to produce high-chromium chromite concen- 
trates. The best concentrate was pro- 
duced from sample E. The grade was 53.8 
pet Cr203 with a Cr:Fe ratio of 2.4:1, 
and the chromium recovery was 87 pet. 
Sample A was concentrated to 48.7 pet 
Cr 2 3 with a Cr:Fe ratio of 2.2:1 and 
64 pet chromium recovery. The grade of 
the concentrate from sample D was 48.8 
pet Cr 2 03 with chromium recovery of 81 
pet and a Cr:Fe ratio of 2.0:1. 

Four samples were beneficiated to pro- 
duce high-iron or marginal high-iron 
chromite concentrates. The grade of the 
concentrate from sample G was 50.1 pet 
0^03 , high enough to be considered a 
high-chromium chromite, but the Cr:Fe 
ratio was only 1.7:1; chromium recovery 
was 89 pet. Sample H was concentrated to 
44.7 pet Cr 2 3 with a Cr:Fe ratio of 
1.5:1 and 87 pet chromium recovery. Con- 
centrates from samples C and J met the 
Cr:Fe ratio requirement, but they were 



TABLE 4. - Summary of the calculated composite concentrates from benef Iciation 
of 11 chromite-bearing samples from the lower Kanuti River and Caribou 
Mountain areas 



Chromite 


Wt-pct 






Analysis, 


pet 




Cr recov- 
ery, pet 


Cr:Fe 


classification 

and sample 


Cr 2 3 


Fe 


MgO 


A1 2 3 


Si0 2 


S 


P 


ratio 


High-chromium : 
E 


79.2 
23.0 
53.2 

76.6 
76.9 

27.4 
23.7 

81.1 

27.9 

84.1 
73.5 


53.8 
48.7 
48.8 

50.1 
44.7 

36.8 
35.8 

27.5 

33.6 

25.3 
23.5 


15.5 
15.3 

16.8 

20.6 
21.0 

15.6 
16.1 

16.8 

16.3 

22.7 
20.3 


12.5 
14.9 
14.3 

10.4 
11.7 

16.6 
16.3 

16.5 

15.8 

14.2 
15.9 


9.4 
10.8 
12.2 

7.9 
13.7 

18.8 
19.1 

33.0 

26.2 

24.4 
28.6 


3.8 
4.2 
2.5 

2.4 
1.6 

5.7 
5.8 

1.0 

3.3 

2.0 
2.3 


0.028 
.020 
.021 


0.01 
.05 
.02 


86.8 
63.9 
80.6 

88.5 
87.3 

64.3 
53.7 

86.0 

73.8 

91.7 
83.7 


2.4 


A 


2.2 


D 


2.0 


High-iron: 
G 


1.7 


H 


1.5 


Marginal high- 
iron: 
C 


1.6 


J 


1.5 


High-aluminum: 
I 


1.1 


Marginal high- 
aluminum: F. 
Subraarginal: 
B 


1.4 
.8 




.8 



NOTE. — Absence of data indicates no analysis. 



significantly below the grade requirement 
of 40 pet Cr203. The metallurgical bal- 
ances in tables A-3 and A-10 show that 
the electrodynamic concentrates could 
possibly be improved enough, with some 
sacrifice in recovery, to raise the com- 
posite grade to near 40 pet Cr 2 03» 

Two samples were beneficiated to pro- 
duce high-aluminum or marginal high- 
aluminum chromite concentrates. The con- 
centrate from sample I was a high- 
aluminum product with a grade of 27.5 pet 
Cr 2 03 and 33.0 pet Al 2 03 and a chromium 
recovery of 86 pet. The concentrate from 
sample F was a marginal high-aluminum 
product with 33.6 pet Cr 2 3 and 26.2 pet 
Al 2 03 with chromium recovery of 74 pet. 

Concentrates from samples B and K had 
Al 2 03 contents of more than 20 pet, but 
the combination of Cr 2 03 and Al 2 03 was 
significantly below 60 pet. The metal- 
lurgical balances in tables A-2 and A-ll 
show that the concentrates cannot be 
upgraded enough to meet the marginal 



high-aluminum classification. They were 
classified as submarginal chromites. 

The gravity concentration products from 
each of the 11 samples were analyzed for 
precious-metals content. Only the table 
concentrates from samples B and G con- 
tained platinum at a level above the min- 
imum detection limit of 0.01 oz/ton. The 
head analysis of sample B indicated the 
presence of 0.039 oz/ton Pt. The calcu- 
lated analysis of the composite concen- 
trate was 0.022 oz/ton Pt , and the cal- 
culated head was 0.021 oz/ton Pt. The 
analyses indicate that the platinum is 
not uniformly distributed in the rock and 
that it may be associated with both the 
chromium mineral and gangue. The head 
analysis of sample G was less than 
0.01 oz/ton Pt, and the calculated anal- 
ysis of the composite concentrate was 
0.01 oz/ton Pt. Examination of these 
11 samples indicated that the chromite- 
bearing areas of the lower Kanuti River 
and Caribou Mountain ultramafics are not 
significant resources for platinum. 



SUMMARY AND CONCLUSIONS 



Eleven samples of chromite-bearing ma- 
terials were collected from three ultra- 
mafic bodies in the Caribou Mountain- 
Melozitna ultramafic belt of central 
Alaska. These samples were characterized 
mineralogically and beneficiated to pro- 
duce chromite concentrates. 

The samples ranged from hard, unweath- 
ered, massive chromite to chromite dis- 
seminated in lenses and stringers. All 
were peridotites or chromitites that con- 
sisted essentially of variable amounts of 
chromite or chromohercynite, olivine, and 
serpentine. 

A benef iciation process was designed to 
treat the samples that included grinding 
and sizing, gravity concentration, and 
electrodynamic separation. Three high- 
chromium (metallurgical-grade) chromite 
concentrates, two high-iron (chemical- 
grade) chromite concentrates, and one 
high-aluminum (refractory-grade) chromite 



concentrate were produced. Three other 
concentrates were marginal, and two con- 
centrates were submarginal. Recoveries 
ranged from 54 to 92 pet ^203. 

Potential platinum association with the 
chromite was investigated. No platinum- 
group minerals were observed in the min- 
eralogical examinations , although in one 
sample the calculated platinum content of 
the gravity concentrate was 0.022 oz/ton. 
The platinum content of the other concen- 
trates was at or below the detection lim- 
it of 0.01 oz/ton. 

This investigation was a preliminary 
evaluation of the chromite and platinum 
resource potential of the lower Kanuti 
River and Caribou Mountain ultramafic 
bodies. Although all of the samples were 
high-graded from surface exposures , they 
indicate that the areas may be signifi- 
cant chromium resources. They do not in- 
dicate good platinum resources. 



10 



APPENDIX. —METALLURGICAL BALANCES 
TABLE A-l. - Gravity concentration and electrodynamic separation of sample A 



Product' 



Wt-pct 



Cr 2 3 



Fe 



Analysis, pet 



MgO 



A1 2 3 



SiO, 



Cr distri- 
bution, pet 



Cr:Fe 
ratio 



48 by 100 mesh: 

Table concentrate* 

Table middlings 

Electrodynamic separation: 
Cleaner concentrate* .... 

Cleaner tailings 

3d rougher middlings.... 
Scavenger concentrate... 

Scavenger tailings 

Table tailings 

100 by 200 mesh: 

Table concentrate* 

Table middlings 

Electrodynamic separation: 
Cleaner concentrate*.... 

Cleaner tailings 

2d rougher middlings.... 
Scavenger concentrate... 

Scavenger tailings 

Table tailings 

Minus 200 mesh: 

Table concentrate* 

Table tailings 

Composite or total 

Calculated composite con- 



2.7 
32.6 

12.1 

.4 
3.7 

.6 
15.8 
11.0 

3.4 
13.6 

1.9 

.3 

.6 

.4 

10.4 

8.3 

2.9 

25.5 



51.2 
24.7 

46.3 
35.4 
36.2 
38.0 
4.9 
4.1 

52.9 
13.5 

48.1 
43.0 
33.0 
43.3 
3.7 
2.4 

51.4 
9.1 



16.0 
10.1 

14.6 
12.0 
12.1 
12.3 
5.9 
5.5 

15.8 
7.6 

15.4 
13.7 
12.4 
14.1 
5.7 
5.1 

16.7 
6.5 



13.2 
31.3 

16.6 



11.0 
6.6 

10.2 



13.3 
42.8 

13.7 



11.4 
3.1 

11.3 



12.4 



11.9 



2.1 
21.7 

5.9 
16.0 
13.9 
13.4 
36.1 
36.7 

2.5 
30.5 

3.9 

8.0 

15.2 

7.3 

37.5 

38.1 

1.7 
32.5 



0.016 



.022 



0.16 



.02 



.018 



.023 



.01 



.02 



.014 



.11 



100.0 



17.5 



8.5 



26.9 



centrate 



23.0 



48.7 15.3 14.9 10.8 



4.3 



020 .05 



7.9 



32.0 
.8 
7.6 
1.3 
4.4 
2.6 

10.3 



5.2 
.7 
1.1 
1.0 
2.2 
1.1 

8.5 
13.3 



100.0 



63.9 



2.2 



2.2 



2.3 



2.1 



2.1 



2.2 



Products with asterisks have been mathematically combined to give the calculated composite 



concentrate. 



TABLE A-2. - Gravity concentration and electrodynamic separation of sample B 



Product 1 



Wt-pct 



Cr 2 3 



Analysis, pet 



Fe 



MgO 



A1 2 3 



SiO, 



Cr distri- 
bution, pet 



Cr:Fe 
ratio 



35.2 
13.3 

9.3 

.2 
1.3 

.2 
2.3 

20.4 
4.2 

1.3 
1.7 
1.2 

17.9 
9.0 



25.3 
19.6 

23*5 
11.0 
16.5 
20.3 
2.4 

26.3 
14.8 

23.8 

15.8 

2.2 

24.8 
14.4 



23.0 
20.0 

22.0 
14.3 
17.4 
20.6 
8.8 

22.6 
16.5 

22.6 

17.3 

8.0 

22.6 
15.6 



12.9 



15.3 



23.6 



27.2 



15.1 



14.8 



15.2 



23.0 



27.8 



26.0 



1.5 
9.3 

2.6 
21.0 
13.1 

7.3 
33.6 

2.0 
16.2 

2.5 
13.9 
33.8 

2.8 
17.1 



100.0 



23.1 



21.4 



4.9 



84.1 



25.3 



22.7 14.2 24.4 



2.0 



100.0 



91.7 



0.8 



48 by 100 mesh: 

Table concentrate* 

Table tailings 

Electrodynamic separation: 

Cleaner concentrate* 

Cleaner tailings 

3d rougher middlings 

Scavenger concentrate 

Scavenger tailings 

100 by 200 mesh: 

Table concentrate* 

Table tailings 

Electrodynamic separation: 

Concentrate* 

Middlings 

Tailings 

Minus 200 mesh: 

Table concentrate* 

Table tailings 

Composite or total 

Calculated composite con- 

centrate 1 

Products with asterisks have been mathematically combined to give the calculated composite 
concentrate. 



38.5 



9.5 
.1 
.9 
.2 
.2 

23.2 



1.3 

1.2 
.1 

19.2 
5.6 



.8 



TABLE A-3. - Gravity concentration and electrodynamic separation of sample C 



11 



Product' 



Wt-pct 



Cr 2 3 



Analysis, pet 



Fe 



MgO 



A1 2 3 



SiO- 



Cr distri- 
bution, pet 



Cr:Fe 
ratio 



14.9 
25.6 

19.0 



20.5 
12.4 

16.7 



15.0 
32.6 

16.1 



20.7 
9.7 

18.4 



15.0 



20.3 



2.7 
18.5 

10.2 
17.9 
14.3 
17.8 
37.3 
36.1 

2.1 
25.7 

5.6 
12.4 
15.5 

9.8 
37.3 
38.7 

2.2 
34.7 



100.0 



15.7 



9.2 



26.1 



27.4 



36.8 



15.6 16.6 18.8 



5.7 



17.2 



20.9 

.6 

9.9 

.8 

2.0 

4.4 

10.4 



7.2 
.8 
.5 
1.4 
1.9 
1.3 

8.6 
12.1 



100.0 



64.3 



1.7 



1.5 



48 by 100 mesh: 

Table concentrate* 

Table middlings 

Electrodynamic separation: 

Cleaner concentrate* 

Cleaner tailings 

3d rougher middlings 

Scavenger concentrate 

Scavenger tailings 

Table tailings 

100 by 200 mesh: 

Table concentrate* 

Table middlings 

Electrodynamic separation: 

Cleaner concentrate* 

Cleaner tailings 

3d rougher middlings 

Scavenger concentrate 

Scavenger tailings 

Table tailings 

Minus 200 mesh: 

Table concentrate* 

Table tailings 

Composite or total 

Calculated composite concen- 

trate 1 

^Products with asterisks have been mathematically combined to give the calculated composite 
concentrate. 



6.7 
22.3 

10.4 

.4 

5.3 

.5 

5.7 

16.7 

3.9 
10.5 

3.1 

.4 

.3 

.7 

6.0 

8.4 

3.3 
28.2 



40.3 
23.2 

31.4 
24.1 
29.4 
24.1 
5.4 
4.2 

41.8 
16.8 

36.2 
29.4 
26.3 
32.3 
5.0 
2.4 

41.1 
6.7 



16.1 
11.8 

14.4 
11.8 
12.0 
11.7 
6.2 
5.9 

16.3 
9.8 

16.2 
13.6 
13.1 
14.1 
6.3 
4.7 

17.3 
6.6 



1.8 



1.5 



1.6 



1.6 



TABLE A-4. - Gravity concentration and electrodynamic separation of sample D 



Product 1 


Wt-pct 


Analysis, pet 


Cr distri- 
bution, pet 


Cr:Fe 




Cr 2 3 


Fe 


MgO 


A1 2 3 


Si0 2 


S 


P 


ratio 


48 by 100 mesh: 
























10.6 
27.3 


49.7 
41.7 


17.1 
15.1 


13.9 
18.8 


12.6 
10.5 


1.8 
8.0 


0.019 


0.01 


16.3 


2.0 






Electrodynamic separation: 






















Cleaner concentrate* .... 


19.7 


47.6 


16.5 


14.7 


12.1 


2.9 


.020 


.03 


29.1 


2.0 




.3 


39.5 


14.8 






9.0 






.4 




3d rougher middlings.... 


2.6 


46.6 


16.0 






3.9 






3.8 




Scavenger concentrate. . . 


.6 


42.4 


15.1 






6.8 






.8 






4.1 


6.9 


6.7 






33.8 






.9 






8.5 


4.2 


5.7 






34.8 






1.1 




100 by 200 mesh: 
























6.4 
12.2 


50.6 
34.2 


17.1 
13.2 


13.8 
25.0 


12.4 
8.6 


1.5 
13.9 


.018 


.01 


10.0 


2.0 






Electrodynamic separation: 






















Cleaner concentrate* .... 


7.1 


49.1 


16.6 


14.0 


11.8 


2.5 


.024 


.02 


10.8 


2.0 




.4 


40.0 


13.6 






11.7 






.5 




2d rougher middlings .... 


.4 


36.4 


14.5 






9.1 






.4 




Scavenger concentrate... 


.3 


44.0 


15.2 






5.9 






.4 






4.0 


6.2 


6.6 






34.8 






.8 






5.1 


2.3 


5.1 






35.7 






.4 




Minus 200 mesh: 
























9.4 
20.5 


49.3 
15.5 


16.8 
8.5 


14.5 


12.3 


2.9 
26.7 


.026 


.01 


14.4 
9.9 


2.0 








100.0 


32.2 


12.7 






14.6 






100.0 




Calculated composite con- 
























53.2 


48.8 


16.8 


14.3 


12.2 


2.5 


.021 


.02 


80.6 


2.0 


1 Products with asterisks ha 


ive beer 


i ma the 


matica 


lly combinec 


to g 


ive tl 


le cs 


ilculated con 


iposite 


concentrate. 























12 



TABLE A-5. - Gravity concentration and electrodynaraic separation of sample E 



Product 1 



48 by 100 mesh: 

Table concentrate* 
Table tailings. . .. 
Elect rodynamic 
separation: 
Cleaner con- 
centrate*. . . . 
Cleaner tail- 
ings 

3d rougher 

middlings. . . . 
Rougher tail- 
ings 

100 by 200 mesh: 
Table concentrate* 
Table tailings .... 
Elect rodynamic 
separation: 
Concentrate* . . 

Middlings 

Tailings 

Minus 200 mesh: 

Table concentrate* 
Table tailings.... 
Composite or 

total 

Calculated com- 
posite concen- 
A 



Wt-pct 



Cr 2 3 



Fe 



Analysis, pet 



MgO 



A1 2 3 Si0 2 



Cr distri- 
bution, pet 



Cr:Fe 
ratio 



42 
7 



1 

1 

16 
3 



.1 
.8 



.5 

.1 

.6 

.6 

.2 
.5 



16 
14 



.2 
.6 
.7 

.2 
.2 



53.8 
34.3 



47.1 

36.8 

28.1 

8.0 

55.0 
24.3 



32.4 

28.4 

5.5 

55.1 
35.5 



15.5 
10.7 



14.0 

11.4 

9.1 

4.4 

15.6 
8.2 



10.6 
9.5 
3.5 

15.8 
11.1 



12.7 



14.9 



9.5 



8.7 



12.4 



23.3 



11.3 



10.1 



6.3 



8.5 



3.9 
16.9 



7.3 

14.2 

20.2 

34.7 

3.2 
23.0 



17.6 
19.9 
36.0 

3.0 
15.9 



0.029 



,039 



0.01 



.02 



.025 



.082 



.023 



.02 



.20 



.01 



46.1 

4.3 

.1 

.9 

.3 

18.1 



.1 

1.5 

.1 

18.2 
10.3 



2.4 



2.3 



2.4 



2.1 



2.4 



100.0 



49.1 



14.3 



6.9 



100.0 



trate 



79.2 



53.8 15.5 12.5 9.4 



3.8 



.028 .01 



86.8 



2.4 



Products with asterisks 
composite concentrate. 



have been mathematically combined to give the calculated 



TABLE A-6. - Gravity concentration and elect rodynamic separation of sample F 



Product 



Wt-pct 



Cr 2 3 



Analysis, pet 



Fe 



MgO 



A1 2 3 



SiO- 



Cr distri- 
bution, pet 



Cr:Fe 
ratio 



100 by 200 mesh: 

Table concentrate*... 

Table tailings 

Electrodynamic sep- 
aration: 

Concentrate* 

Middlings 

Tailings 

Minus 200 mesh: 

Table concentrate* ... 

Table tailings 

Composite or total. 
Calculated compo- 



18.3 
34.5 



1.4 

5.8 

27.3 

8.2 
39.0 



33.9 
4.2 



24.4 

10.3 

1.9 

34.2 
5.6 



15.6 
7.4 



15.4 
9.7 
6.4 

18.1 
7.9 



15.9 



19.9 



15.0 



27.9 



23.5 



22.9 



3.0 
27.7 



8.1 
21.7 
29.4 

3.3 
26.3 



49.0 



2.7 
4.7 
4.1 

22.1 
17.4 



1.5 



1.1 



1.3 



100.0 



12.7 



9.9 



20.5 



100.0 



site concentrate 



27.9 



33.6 



16.3 15.8 26.2 



3.3 



73.8 



1.4 



Products with asterisks have 
composite concentrate. 



been mathematically combined to give the calculated 



13 



TABLE A-7. - Gravity concentration and electrodynamic separation of sample G 



Product ' 


Wt-pct 


Analysis, 


pet 






Cr distri- 
bution, pet 


Cr:Fe 




Cr 2 3 


Fe 


MgO 


A1 2 3 


S10 2 


S 


P 


ratio 


48 by 100 mesh: 


34.4 
6.1 

2.2 

.1 

2.3 
1.5 

21.6 
4.8 

.8 
1.1 
2.9 

17.6 
15.5 


49.5 
22.7 

42.8 
31.6 

18.6 
4.3 

51.0 
17.4 

41.7 

32.7 

3.1 

51.6 
26.2 


20.4 
12.3 

19.0 
15.0 

11.0 
6.5 

20.7 
10.6 

18.3 

15.5 

6.9 

21.1 
13.3 


10.7 
13.3 

10.2 
14.1 

9.4 


7.4 
7.8 

8.3 
7.9 

8.2 


2.6 

21.4 

7.3 
15.8 

24.3 
34.6 

2.0 
25.4 

7.7 
14.2 
33.4 

1.7 
19.0 


0.020 
.041 

.018 
.040 

.017 


0.01 
.13 

.01 
.03 

.01 


39.2 

2.2 
.1 

1.0 
.1 

25.4 

.8 
.8 
.2 

20.9 
9.3 


1.7 


Electrodynamic separation: 
Cleaner concentrate* .... 

2d rougher middlings 
plus scavenger concen- 


1.5 


100 by 200 mesh: 


1.7 


Electrodynamic separation: 


1.6 






Minus 200 mesh: 


1.7 








100.0 


43.4 


18.6 






7.0 






100.0 




Calculated composite con- 


76.6 


50.1 


20.6 


10.4 


7.9 


2.4 


.020 


.01 


88.5 


1.7 



Products with asterisks have been mathematically combined to give the calculated composite 



concentrate. 

2 2d rougher middlings, 95 pet; scavenger concentrate, 5 pet. 



TABLE A-8. - Gravity concentration and electrodynamic separation of sample H 



Product 1 


Wt-pct 


Analysis, pet 


Cr distri- 
bution, pet 


Cr:Fe 




Cr 2 3 


Fe 


MgO 


A1 2 3 


Si0 2 


ratio 


48 by 100 mesh: 


39.8 
5.0 

1.2 
.6 

1.0 
2.2 

20.7 
4.1 

.3 

.9 

2.9 

14.9 
15.5 


43.8 
22.4 

39.2 
29.5 

34.5 
5.3 

46.0 
14.3 

37.6 

29.7 

7.6 

45.7 
25.0 


20.8 
13.0 

19.5 
15.7 

17.5 
6.4 

21.3 
9.5 

18.9 

16.0 

6.9 

21.2 
14.0 


11.9 
13.6 

11.8 
15.3 

10.6 


12.4 
11.9 

15.0 
12.4 

15.7 


1.8 
19.2 

5.3 
13.2 

8.9 
33.0 

1.2 
26.5 

6.3 
12.5 
31.5 

1.1 
16.9 


44.3 

1.2 
.4 

.9 
.3 

24.2 

.3 
.7 
.6 

17.3 
9.8 


1.4 






Electrodynamic separation: 


1.4 


3d rougher middlings plus 




100 by 200 mesh: 


1.5 


Electrodynamic separation: 


1.4 


Middlings 








Minus 200 mesh: 


1.5 








100.0 


39.4 


19.1 






5.8 


100.0 




Calculated composite concen- 


76.9 


44.7 


21.0 


11.7 


13.7 


1.6 


87.3 


1.5 



Products with asterisks have been mathematically combined to give the calculated composite 

; scavenger concentrate, 7 pet. 



concentrate. 

2 3d rougher middlings, 93 pet 



14 

TABLE A-9. - Gravity concentration and electrodynamic separation of sample I 


Product 1 


Wt-pct 


Analysis, pet 


Cr distri- 
bution, pet 


Cr:Fe 


Cr 2 3 


Fe 


MgO 


A1 2 3 


Si0 2 


ratio 


48 by 100 mesh: 


47.4 
6.4 

.8 
3.9 

1.7 

19.4 
2.5 

.5 
1.0 
1.0 

13.0 
11.3 


26.7 
17.8 

24.6 

22.8 

2.8 

29.2 
17.1 

25.7 

21.9 

4.2 

28.1 
21.6 


16.8 
12.3 

16.0 

14.9 

4.1 

16.7 
11.6 

16.6 

14.8 

5.1 

17.1 
14.6 


16.5 
17.4 

16.7 
16.3 

16.1 


32.5 
31.5 

34.5 
32.9 

32.5 


1.0 
11.5 

3.2 

5.5 

28.7 

1.1 
13.5 

1.9 

6.4 

28.5 

.7 
9.3 


48.8 

.8 

3.4 

.2 

21.8 

.5 
.8 
.2 

14.1 
9.4 


1.1 


Electrodynamic separation: 


1.0 


100 by 200 mesh: 


1.2 






Electrodynamic separation: 


1.1 






Minus 200 mesh: 


1.1 


Calculated composite con- 




100.0 


26.0 


16.1 






2.9 


100.0 




81.1 


27.5 


16.8 


16.5 


33.0 


1.0 


86.0 


1.1 


Products with asterisks have 
site concentrate. 


been ma 


themati 


cally 


combined to give the 


calculated compo- 



TABLE A-10. - Gravity concentration and electrodynamic separation of sample J 



Product 



48 by 100 mesh: 

Table concentrate* 

Table middlings 

Electrodynamic separation: 
Cleaner concentrate* .... 

Cleaner tailings 

3d rougher middlings.... 
Scavenger concentrate... 

Scavenger tailings 

Table tailings 

100 by 200 mesh: 

Table concentrate* 

Table middlings 

Electrodynamic separation: 
Cleaner concentrate* .... 

Cleaner tailings 

2d rougher middlings.... 

Rougher tailings 

Table tailings 

Minus 200 mesh: 

Table concentrate* 

Table tailings 

Composite or total 

Calculated composite con- 



centrate 



Wt-pct 



4.9 
21.7 

11.1 

.5 

5.2 

.8 

4.1 

16.4 

3.8 
13.0 

2.5 
.5 
1.2 
8.8 
6.9 

1.4 
31.9 



100.0 



Products with asterisks have 
site concentrate. 



Cr 2 3 



39.5 
25.7 

32.6 
27.3 
25.9 
28.9 
9.5' 
5.4 

39.0 
15.5 

35.8 

31.3 

24.6 

7.8 

2.1 

39.9 
9.5 



15.8 



23.7 35.8 16.1 16.3 



Analysis, pet 



Fe 



16.8 
13.0 

15.2 
13.9 
11.8 
14.0 
7.4 
6.4 

17.3 
10.2 

16.6 

15.0 

12.9 

7.5 

4.9 

17.3 
7.8 



9.7 



MgO 



14.5 
23.0 

18.1 



14.0 
32.2 

16.0 



15.0 



A1 2 3 Si0 2 



20.7 
11.4 

17.3 



21.3 
8.8 

20.2 



20.3 



19.1 



2.4 
15.9 

8.9 
14.1 
17.1 
12.5 
33.6 
34.9 

2.2 
26.1 

5.2 

9.7 

16.9 

34.5 

38.5 

3.4 
32.3 



25.8 



5.8 



Cr distri- 
bution, pet 



12.2 



22.9 
.9 
8.5 
1.5 
2.5 
5.6 

9.4 



5.7 
1.0 
1.9 
4.3 
.9 

3.5 
19.2 



100.0 



53.7 



Cr:Fe 
ratio 



1.6 



1.5 



1.5 



1.5 



1.6 



1.5 



been mathematically combined to give the calculated compo- 



15 



TABLE A-ll. - Gravity concentration and electrodynamic separation of sample K 



Product 1 



Wt-pct 



Analysis, pet 



Cr 2 03 Fe MgO AI2O3 



SiO- 



Cr distri- 
bution, pet 



Cr:Fe 
ratio 



48 by 100 mesh: 

Table concentrate* 

Table tailings 

Electrodynamic separa- 
tion: 
Cleaner concentrate*.. 

Cleaner tailings 

3d rougher middlings.. 
Scavenger concentrate. 
Scavenger tailings .... 
100 by 200 mesh: 

Table concentrate* 

Table tailings 

Electrodynamic separa- 
tion: 
Cleaner concentrate*.. 

Cleaner tailings 

3d rougher middlings.. 
Scavenger concentrate. 
Scavenger tailings .... 
Minus 200 mesh: 

Table concentrate* 

Table tailings 

Composite or total 

Calculated composite 



concentrate 



39.4 
10.5 



5.8 
.1 

1.9 
.2 

2.5 

16.4 
7.4 



4.0 
.2 
.3 
.2 

2.7 

7.9 
18.4 



100.0 



73.5 



23.7 
14.9 



22.9 
16.8 

9.7 
19.7 

2.0 

23.2 

14.6 



22.8 
17.8 
11.0 
19.3 
2.2 

24.8 
15.8 



20.4 
15.9 



19.7 
16.6 
12.8 
18.0 
8.4 

20.3 
15.7 



20.0 
17.2 
14.4 
18.0 
8.5 

20.8 
15.8 



16.0 



16.7 



28.5 



29.8 



16.3 



15.7 



29.2 



30.1 



14.2 



32.0 



2.3 
14.3 



3.4 
12.1 
22.4 

8.1 
33.4 

2.5 
14.9 



2.8 
10.3 
20.1 

8.0 
33.2 

1.3 
13.9 



20.7 



18.7 



6.6 



23.5 20.3 15.9 29.2 



2.4 



45.0 



6.4 
.1 
.9 
.2 
.2 

18.4 



4.4 
.2 
.2 
.2 
.3 

9.5 

14.0 



100.0 



83.7 



0.8 



.8 



.8 



.8 



Products with asterisks have been mathematically combined to give the calculated 



composite concentrate. 



INT.-BU.OF MINES.PGH..PA. 26786 






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